Control-cage, a centrifugal shot-blasting device, and a centrifugal shot-blasting device for throwing abrasive grains

ABSTRACT

A control-cage that can concentrate the distribution of shot-blasting media, a centrifugal shot-blasting device using this control-cage, and a centrifugal shot-blasting device for throwing abrasive grains, are provided. 
     This control-cage is used for a centrifugal shot-blasting device that rotates an impeller having a plurality of blades at high speed, and that throws shot-blasting media at an object to be processed through the opening of the control-cage by means of the blades. The control-cage is cylindrically shaped and is placed inside the impeller. The opening of the control-cage is made by cutting out the cylindrical part of it in parallel with its central axis. Also, the opening has a quadrangular shape, and has lateral walls located upstream and downstream of the direction of the rotation of the impeller. The upstream wall is made so that the angle between a plane containing the axis and the plane containing both the axis and the inner edge of the upstream wall is larger than the angle between the plane containing the axis and the plane containing both the axis and the outer edge of the upstream wall when they are measured in the direction opposite to the direction of the rotation of the impeller.

FIELD OF INVENTION

The present invention relates to a control-cage, and a centrifugal shot-blasting device and a centrifugal shot-blasting device for throwing abrasive grains, using this control-cage. More particularly, it relates to a control-cage that rotates an impeller having a plurality of blades at high speed, and throws shot-blasting media that are discharged through the opening of the control-cage at an object to be processed, as well relating to a centrifugal shot-blasting device and the device for throwing abrasive grains using this control-cage. The control-cage can concentrate the distribution of shot-blasting media.

BACKGROUND OF THE INVENTION

Usually, a shot blasting is carried out so as to flake and remove the rust, burrs, scales, paint, etc., on the surface of an object to be processed by throwing shot-blasting media against it. At the shot blasting, a centrifugal shot-blasting device is used. It rotates an impeller having a plurality of blades at high speed, and causes them to throw the media centrifugally. In this device, the shot-blasting media that through an inlet tube are stirred by a rotating distributor, and discharged through an opening of a cylindrical control-cage, and then thrown out from the outer edge of the blades against the object to be processed.

The opening is made on the cylindrical part of the control-cage in the shape of a triangle or a quadrangle, so as to control the angle of emission or the angle of spray, as disclosed in the Publication of Examined Japanese Patent Application No. S50-32142 and Japanese Patent Laid-open No. H09-174437, for example. In a cross-section of the control-cage, the shape of the triangle or the quadrangle is like the Japanese character for “ha,” but upside down (the shape of the letter V). In general, it is known that through a quadrangular opening shot-blasting media are concentrically thrown, and through a triangular opening they are uniformly and widely thrown, against an object.

Although through a quadrangular opening the shot-blasting media are usually concentrically thrown against an object, if, for example, the object to be processed is small, not all the media will be effectively used, because some of them will be thrown at spaces other than the object. Therefore, some media will be useless. Also, the shot-blasting media that are thrown against spaces other than the object cause the liner inside a housing (case) to be badly worn. Therefore, too much material for a liner is needed (for example, to make it thicker, or to use abrasion-resistant steel, which is expensive, instead of rolled steels for general structure, which is usually used, as the material of the liner). Accordingly, it has a problem in that it requires more money. Further, it has problems in that the frequency of maintenance, such as exchanging parts, is increased and the cost for the exchanges is increased, because the wear of the liner is greater.

To concentrically throw the media, it is possible to make the area of the quadrangular opening of the control-cage small. Even when made small, since the shot-blasting media contacts the downstream side of the opening (downstream of the direction of the rotation of the impeller) when they are thrown through it, the media are widely spread, and the area at which they are thrown (throwing distribution) is widened.

Also, as in FIG. 3 of the Publication of Examined Japanese Patent Application No. S50-32142 and in FIG. 1 of Japanese Patent Laid-open No. H09-174437, an exit for the discharge of abrasive grains is made on the body of the control-cage. The lateral wall of the exit is located upstream of the direction of the rotation of the distributor. The lateral wall of the exit is located downstream. Both are located on planes that extend from the shaft axis of the control-cage. Thus, usually the exit is made so as to widen toward the end.

The area at which abrasive grains are thrown in a fan-like form is widened more than necessary, when using the conventional centrifugal shot-blasting device for throwing abrasive grains and using this structure of an exit for discharging the grains. Accordingly, they are not effectively thrown against the object to be processed. Therefore, depending on the kind of object, many abrasive grains do not hit it, and the efficiency of throwing abrasive grains is decreased.

SUMMARY OF THE INVENTION

Thus, the object of the present invention is to provide a control-cage that can concentrate the distribution of shot-blasting media and a centrifugal shot-blasting device that uses this control-cage.

Also, the object is to provide a centrifugal shot-blasting device for throwing abrasive grains that can narrow the area at which the grains are thrown in a fan-like form.

The feature of the invention of claim 1 is a control-cage used for a centrifugal shot-blasting device that rotates an impeller having a plurality of blades at high speed, and throws shot-blasting media against the object to be processed through the opening of the control-cage by the blades. The control-cage is cylindrically shaped. It is placed in the internal space of the impeller. The opening of the control-cage is made by cutting out the cylindrical part of it in parallel with its central axis. Also, the opening has a quadrangular shape, and has a lateral wall located upstream of, and a lateral wall located downstream of, the direction of the rotation of the impeller. The upstream wall is made so that the angle between a plane containing the axis and the plane containing both the axis and the inner edge of the upstream wall is larger than the angle between the plane containing the axis and the plane containing both the axis and the outer edge of the upstream wall when they are measured in the direction opposite that of the rotation of the impeller.

Since the control-cage is constructed as above, the upstream wall is basically directed to the object to be processed. So the flow of the shot-blasting media discharged through the opening of the control-cage can be directed to the object. Accordingly, it can concentrate the distribution of the shot-blasting media thrown to a given object to be processed. Therefore, it can treat a small object without wasting shot-blasting media, and can reduce the frequency of the maintenance of the inner liner and can reduce the cost of the parts. Further, since the density of the media at the place to shot-blast is increased, the processing time can be shortened.

Preferably, the upstream wall and the downstream wall should be parallel to each other.

Preferably, the upstream wall is made so that it would correspond to the tangential line of the inner periphery of the control-cage if the control-cage were to be cut radially.

Preferably, the downstream wall is made so that the angle between the plane containing the axis and the plane containing both the axis and the inner edge of the downstream wall is larger than the angle between the plane containing the axis and the plane containing both the axis and the outer edge of the downstream wall when they are measured in the direction opposite to the direction of the rotation of the impeller.

Preferably, the downstream wall is made so that the angle between the plane containing the axis and the plane containing both the axis and the inner edge of the downstream wall is larger than the angle between the plane containing the axis and the plane containing both the axis and the outer edge of the downstream wall when they are measured in the direction opposite to the direction of the rotation of the impeller. Further, the difference between the angles should be 0-35 degrees, in which one angle is between the plane containing the axis and the plane containing both the axis and the outer edge of the upstream wall and the other is between the plane containing the axis and the plane containing both the axis and the inner edge of the downstream wall.

Also, the centrifugal shot-blasting device of the present invention is characterized by comprising a housing, a driving means, an impeller, a distributor, the control-cage of claim 1, and an inlet tube. The driving means is installed outside of a lateral side of the housing. The impeller has a plurality of blades and is fitted onto the driving shaft of the driving means. The distributor is placed inside the impeller. It is concentrically fitted onto the driving shaft. Also, it has openings in its circumference almost equally spaced from each other. The end of the control-cage is fitted on an inlet that is provided at a lateral side of the housing. The inlet tube is fixed on the housing so as to cause shot-blasting media to be supplied to the inlet.

Further, the plane that includes the central axis in the present invention represents one that includes the axis and that does not intersect with an opening that is surrounded by an upstream wall and a downstream wall.

Preferably, the impeller comprises a lateral plate on the side of the driving shaft of the driving means, a lateral plate that is located on the side of the inlet tube and apart form the lateral plate on the side of the driving shaft at given distance, and a plurality of blades. The lateral plate located on the side of the inlet tube has an opening at its center that is larger than the circumference of the control-cage. The blades are radially fixed between the lateral plates on the side of the inlet tube and on the side of the driving shaft.

The feature of the invention of claim 8 is a centrifugal shot-blasting device for throwing abrasive grains that comprises an impeller, a control-cage, and a distributor. The impeller can rotate. It has a space in its middle that is cylindrical. The control-cage is nearly cylindrical. It is fixed inside that space. Further, it has an exit for abrasive grains on its cylindrical part, to discharge the grains. The distributor is located inside the control-cage, so that it can be rotated together with the impeller. The exit for abrasive grains on the control-cage is approximately an elongated slit that has a given width. It is parallel to the central axis of the control-cage. Also, it has an upstream wall, which is located upstream of the direction of rotation of the distributor, and a downstream wall, which is located downstream of the direction of rotation of it. The upstream wall is inclined in the direction of the rotation of the distributor at 30-90 degrees to a line that is orthogonal to the central axis and that crosses the inner edge of the upstream wall.

In this device, the abrasive grains that are agitated and driven by the distributor are supplied to the exit for them. Then the abrasive grains are prevented from directly passing through the exit in the radial direction of the control-cage by the surface of the inner wall (upstream wall) of the exit. This wall is located behind the direction of the rotation of the distributor (upstream of the direction of the rotation). The grains are discharged onto the blades of the impeller. As a result of this, since the abrasive grains are so discharged, and are restrained from flying apart through the exit for the abrasive grains, the area at which the grains are thrown by the impeller in a fan-like form can be narrower than that of the conventional area.

The feature of the invention of claim 9 is a centrifugal shot-blasting device for throwing abrasive grains that comprises an impeller, a control-cage, and a distributor. The impeller can rotate and has a space shaped as a cylinder in its middle. The control-cage is nearly cylindrical in shape and fixed inside the space. Further, it has an exit for abrasive grains on its cylindrical part, to discharge them. The distributor is located inside the control-cage so that it can be rotated together with the impeller. The exit for the abrasive grains on the control-cage is approximately an elongated slit that has a given width. It is parallel to the central axis of the control-cage. Also, it has an upstream wall, which is located upstream of the direction of the rotation of the distributor, and a downstream wall, which is located downstream of the direction of the rotation of it. The upstream wall runs along the almost tangential line of the inner periphery of the control-cage.

In this device, the abrasive grains that are agitated and driven by the distributor are smoothly pushed into the exit for the abrasive grains guided by the surface of the inner wall (upstream wall) of the exit, which wall runs along the almost tangential line of the inner periphery of the control-cage. Accordingly, the grains that are pushed into the exit converge there. Thus they are moved through the exit and onto the blades of the impeller in a high density. As a result, the area at which the grains are thrown by the impeller in a fan-like form can be narrower than that of a conventional area.

Preferably, the upstream wall is inclined to the direction of the rotation of the distribution at 30-90 degrees to the line that is orthogonal to the central axis and that crosses the inner edge of the upstream wall. If the incline is less than 30 degrees, the abrasive grains are not sufficiently prevented from directly passing through the exit in the radial direction of the control-cage.

Preferably, the downstream wall is inclined to the direction of the rotation of the distribution at 30-90 degrees to the line that is orthogonal to the central axis and that crosses the inner edge of the downstream wall. If the incline is less than 30 degrees, the abrasive grains will be diffused, because they will hit the wall when they pass through the exit.

By making the downstream wall approximately in parallel with the upstream wall, the direction the abrasive grains run can be restricted and the area at which the grains are thrown can be narrow.

Preferably, the given width of the exit for the abrasive grains is determined so that the angle between the line that is orthogonal to the central axis and that crosses the outer edge of the upstream wall and the line that is orthogonal to the central axis and that crosses the inner edge of the downstream wall is 0-35 degrees. If the angle is less than 0 degrees, the inner wall in the front side (downstream side) and the inner wall in the rear side (upstream wall) of the exit will impede the abrasive grains from passing through the exit. Accordingly, the grains will accumulate at the exit, and block it, or the maximum quantity of the thrown grains will decrease. If the angle is more than 35 degrees, the area of the opening of the exit will become wide, and the abrasive grains that pass through the exit will be so widely diffused that the area where the grains are thrown will be widened.

The elongated slit of the exit for the abrasive grains includes a quadrangular opening.

DESCRIPTIONS OF THE PREFERRED EMBODIMENT Embodiment 1

Now we discuss a control-cage and a centrifugal shot-blasting device using this control-cage, by referring to the drawings. As in FIG. 1, the centrifugal shot-blasting device of the present invention comprises a housing (impeller case) 2, a driving means 3, an impeller 4, a distributor 5, a control-cage 6, and an inlet tube 7. The housing 2 is placed on an upper wall 1 of a polishing chamber for the device. The driving means 3 is placed on the wall 1 and installed outside a lateral side 2 a of the housing 2. The impeller 4 is fitted onto the driving shaft 3 a of the driving means 3. The distributor 5 is placed in a space S that is inside the impeller 4. The distributor 5 is positioned coaxially with the driving shaft 3 a. The control-cage 6 is fixed on the opposite lateral side 2 b of the side 2 a of the housing 2. The inlet tube is fixed on the side 2 b of the housing 2.

The driving means 3 may be a driving motor that has a bearing (not shown). The bearing rotatably supports the driving shaft 3 a. If the shaft 3 a is rotatably supported by a bearing of a bearing unit, the driving means 3 may also comprise the bearing unit, a pulley that is connected to the end of the shaft 3 a, a driving motor, a pulley that is connected to the driving motor, and a belt that is wound on both pulleys.

The impeller 4 is fixed on the driving shaft 3 a by bolts 11 via a hub 10. It comprises a lateral plate 12 a that is on the side of the driving shaft 3 a of the driving means 3, a lateral plate 12 b that is placed apart from the lateral plate 12 a at a given distance, and a plurality of blades 13, e.g., 4-12 blades, that are radially fixed between the lateral plates 12 a and 12 b. The lateral plate 12 b has an opening at its center that is larger than the circumference of the control-cage 6. The plate 12 b and the blades 13 are arranged so that the inner end of the plate 12 b is located at the same location as are the inner ends of the blades 13. The lateral plate 12 a of the impeller 4 and the hub of this embodiment are made as separate items. However, the present invention is not restricted to this, but the plate 12 a and the hub 10 may be made as one item.

The distributor 5 is a part that agitates the shot-blasting media and that is fixed on the lateral plate 12 a by bolts 14. It has more or less or the same number of openings (notches) 15 as do the blades 13, which blades 13 are arranged with almost equal intervals in the circumferential direction. The distributor 5 of this embodiment has comb-like projections, i.e., the same number of nails 16 protrude from a base 5 a in parallel with the central axis of the impeller 4. However, the present invention is not restricted to this. Namely, the ends of the nails 16 may be connected to each other so as to be reinforced.

As in FIGS. 1 and 2, the control-cage 6 is a part that controls the direction of the shot-blasting media by an opening 17 that is made on the cylindrical part in a direction that is parallel to the central axis C (i.e., horizontally in FIG. 1, or perpendicular to the sheet of FIG. 2). The control-cage 6 is located between the distributor 5 and the blade 13. Its back end 6 b is fixed on the circumference of an inlet 18 of the media. The inlet 18 is made at the lateral side 2 b, which is opposite the lateral side 2 a of the housing 2. In this embodiment, as a structure for mounting the control-cage 6, a flange (ring) 19 for linking is set on the inlet 18 and fixed to the lateral side 2 b by bolts 20. Then the protruding part 6 c, formed on the back end 6 b of the control-cage 6, which part is inserted along the inner periphery of the flange 19, is held between the end-face of the flange 19 and the end-face of the inlet tube 7. Finally, they are pushed by the member 21 for clamping the inlet tube, and fixed by bolts 22.

The opening 17 is shaped like a quadrangle where it has an upstream wall 31, which wall is located upstream of the direction of rotation A of the impeller 4, and where it has a downstream wall 32, which is located downstream of the direction of the rotation A of it. The angle θ1 a is measured from the direction opposite to the direction of the rotation A of the impeller 4 from the plane (plane C1) that contains the central axis C and that does not intersect any part surrounded by the upstream wall 31 and the downstream wall 32 to the inner edge 31 a of the upstream wall 31. That angle θ1 a is larger than the angle θ1 b, which is the angle that is measured from the plane C1 to the outer edge 31 b of the upstream wall 31. The angle θ2 a, which is the angle that is measured from the plane C1 containing the central axis C to the inner edge 32 a of the downstream wall 32, is larger than the angle θ2 b, which is the angle that is measured from the plane C1, containing the central axis C, to the outer edge 32 b of the downstream wall 32. Namely, if the control-cage 6 were to be cut radially, the upstream wall 31 would be more inclined to the direction A of the rotation of the impeller 4 than would be the line that connects the inner edge 31 a of the upstream wall 31 to the central axis C. Also, the downstream wall 32 is inclined to the direction A more than is the line connecting the inner edge 32 a of the downstream wall 32 to the central axis C. The relationship between the angles at the upstream wall 31 and that between those at the downstream wall 32 can be accordingly chosen by considering, for example, the mean diameter of the grains, the area of the grains thrown at an object to be processed, the quantity of the thrown grains, the velocity of the grains, etc. Accordingly, the upstream wall 31 is basically aimed at an object to be processed. The downstream wall 32 hardly prevents the flow of shot-blasting media. Therefore, the shot-blasting media that pass through the opening of the control-cage can be guided, so that the flow of them can be basically aimed at the object to be processed. Accordingly, they are concentrated in the area of the given object to be processed. Therefore, a small object can be processed without wasting shot-blasting media. Also, the frequency of the maintenance of the inner liner of the device and the cost of parts can be reduced. Further, the time for processing can be reduced, because the density of the quantity of the thrown media is increased.

As discussed above, because of the relationship of the angles at the upstream wall 31 (θ1 a>θ1 b), if only the upstream wall 31 is inclined to the direction A, the angle θ2 a, which is the angle that is measured from the plane C1 containing the central axis C to the inner edge 32 a of the downstream wall 32, may be the same as the angle θ2 b, which is the angle that is measured from the plane C1 containing the central axis C to the outer edge 32 b of the downstream wall 32. Even in this case, the downstream wall 32 hardly prevents the flow of shot-blasting media.

As for the opening 17, preferably the upstream wall 31 and the downstream wall 32 are in parallel. If so, the thrown shot-blasting media are prevented from being widely distributed. If not, the media may contact the downstream wall 32, and then they are widely distributed. Preferably an opening 47 has the downstream wall 42, which is parallel to the plane C1, as in FIG. 3, and the upstream wall 41, which is made by drawing a tangent line L on the inner circle (inner periphery) 46 a, which line L is parallel to the plane C1, causing the contact point of the line L to be an inner edge 42 a, and causing an upstream wall 41 to be on the tangent line L.

Preferably the difference Δθ(=θ1 b−θ2 a) between the angles θ1 b and θ2 a is 0-35 degrees. The angle θ1 b is the angle that is measured from the plane C1, containing the central axis C, to the outer edge 41 b of the upstream wall 41. The angle θ2 a is the angle that is measured from the plane C1, containing the central axis C, to the inner edge 42 a of the downstream wall 42. If the difference Δθ is less than 0, the opening will be so small that it can be clogged, and so the maximum quantity of the thrown media will be decreased. Also, if the difference Δθ is more than 35 degrees, the opening will be so wide that the area against which they are thrown (the distribution of them) can be widened.

The inlet tube 7, through which shot-blasting media are supplied to the impeller 4, is fixed on the lateral side 2 b of the housing 2 so that the media can be conducted to the inlet 18.

In this embodiment, the shot-blasting media are supplied from the inlet tube 7, pass through the control-cage 6, and are agitated by the rotation of the distributor 5. The media that have been agitated in the control-cage 6 are exhausted through its opening 17 and supplied to the inner edges of the rotating blades 13. Then the shot-blasting media are gradually accelerated by the rotating blades 13, are projected from the outer edges, and remove the rust, burrs, scales, paint, etc., on the surface of an object to be processed. Further, in this embodiment, as discussed above, the angle θ1 a for the opening 17 is larger than the angle θ1 b. Accordingly, since the distribution of the thrown media is concentrated, the wasting of the media decreases, no redundant liner is necessary, and early abrasion is avoided. Also, since the density of the media at the place to shot-blast is increased, the processing time can be shortened.

We now discuss an example of the present invention, but the invention is not restricted to this example.

Example

In this example, as in FIG. 3, a centrifugal shot-blasting device using a control-cage was used. The control-cage has an opening that has an upstream wall 41 and a downstream wall 42. These walls are parallel. Also, the walls are made so that the difference Δθ (=θ1 b−θ2 a) between the angles θ1 b and θ2 a is zero. The angle θ1 b is measured from the plane C1, containing the central axis C, to the outer edge 41 b of the upstream wall 41. The angle θ2 a is measured from the plane C1, containing the central axis C, to the inner edge 42 a of the downstream wall 42. A test of throwing by this device using SB10 (shot-blasting media made by Sintobrater Co., Ltd.), having an average diameter of 1 mm was carried out, and their distribution (an example) was examined. The result is shown in FIG. 4. The same test of throwing by a device using two conventional types of a control-cage was carried out. One cage had an opening of which the shape of the triangle or the quadrangle is like the Japanese character for “ha,” but upside down (the shape of the letter V), and the angle θ of the opening 107 was 40 degrees and the other was 15 degrees (comparative examples 1 and 2), wherein the angle θ was defined as in FIG. 5. In comparative examples 1 and 2, the position of the opening relative to the impeller was almost the same as that of the example. The result is also shown in FIG. 4.

In FIG. 4, as shown by comparative example 1, when the angle of the opening was 40 degrees, the distribution of the thrown media was like a mountain with a gradual slope. As shown by comparative example 2, even when the angle was 15 degrees, the distribution was widely spread, because the shot-blasting media hit the edges of the opening when they were exhausted through it. In contrast, in the example, the distribution was concentrated.

From the results of the distribution of the thrown media as in FIG. 4, one can see that a half-value breadth of the distribution is defined as the area between the angles at which the rate of the thrown media is 50% of the peak value. The half-value breadth of the distribution of comparative example 1 is 49.9 degrees. That of comparative example 2 is 86.6 degrees. In contrast, that of the example is 34.4 degrees. Therefore, the degree of the distribution of the example was 31% less than that of comparative example 1, or 60% less than that of comparative example 2.

Embodiment 2

Now, we discuss an embodiment of the centrifugal shot-blasting device for throwing abrasive grains of the present invention, by referring to FIGS. 6-10. The device comprises an impeller 53, a control-cage 55, and a distributor 56, as in FIG. 8. The impeller 53 is rotatably installed in the device, has a plurality of blades in a radial pattern, and has a cylindrical space 52 in its center. The control-cage 55 is placed in the cylindrical space 52, has a shape of a hollow cylinder, and has an opening 54 for an exit of the abrasive grains, on its lateral side. The distributor 56 is installed in the hollow space of the cage 55 so that it can rotate with the impeller 53.

The exit of the abrasive grains 54 on the control-cage 55 is approximately an elongated slit that has a given width and that is parallel to the central axis 59 of the control-cage 55, as in FIG. 7. As in FIG. 6, it has an inner wall (upstream wall) 58, which is located opposite (upstream of) the direction of the rotation of the distributor 56 (the direction of an arrow 57). The upstream wall 58 is inclined to the direction of the arrow 57 at 70 degrees to the line 60, which is orthogonal to the central axis 59 of the control-cage 55 and that crosses the inner edge of the upstream wall 58.

The inner wall 61 of the exit of the abrasive grains 54, which wall is located forward of the direction of the arrow 57, is approximately parallel to the inner wall (upstream wall) 58.

In the device of this construction, when abrasive grains are supplied into the distributor 56 while the impeller 53 and the distributor 56 are rotating in the direction of the arrow 57, the abrasive grains that are agitated and driven by the distributor are supplied to the exit 54 for the abrasive grains. The abrasive grains are prevented from directly passing through the exit 54 in the radial direction of the control-cage 55 by the surface of the inner wall (upstream wall) 58 of the exit 54. Thus they pass through the exit 54 onto the blades 51 of the impeller 53. As a result of this, they are discharged onto the blades 51 of the impeller 53, while being restrained from flying apart through the exit 54 for the abrasive grains. Accordingly, the area at which the grains are thrown by the impeller 53 in a fan-like form can be narrower than that resulting from a conventional impeller.

In this embodiment, the inner wall (upstream wall) 58 of the exit for the abrasive grains 54 is inclined to the direction of the arrow 57 at 70 degrees to the line 60 that is orthogonal to the central axis 59 of the control-cage 55 and that crosses the inner edge of the upstream wall 58. However, it is not restricted to this shape. As in FIG. 9, the inner wall (upstream wall) 78 of the exit of the abrasive grains 74 of a control-cage 75, which wall is located opposite to (upstream of) the direction of the arrow 57, may be formed as a plane that runs along an almost tangential line of the inner periphery of the control-cage 75. Also, the exit 74 of the abrasive grains on the control-cage 75 may be approximately an elongated slit that has a given width and that is parallel to the central axis 79 of the control-cage 75.

The inner wall (upstream wall) 78 of the exit 74 of the abrasive grains is approximately parallel to the inner wall (downstream wall) 81 of the exit 74. The downstream wall 81 is located forward of the direction of the arrow 57. As in FIG. 9, the given width of the exit 74 is determined such that the angle made by lines 91 and 92 is 0-35 degrees. In the same way as discussed above, the line 91 connects the central axis O of the control-cage 75 and the outer edge (the border at the outside) A of the inner wall (upstream wall) 78 of the exit 74 of the abrasive grains. The line 92 connects the central axis O and the inner edge (the border at the inside) B of the inner wall (downstream wall) 81 of the exit 74.

In the device of this construction, when abrasive grains are supplied into the distributor 56 while the impeller 53 and the distributor 56 are rotating in the direction of the arrow 57, the abrasive grains that are agitated and driven up by the distributor 56 are smoothly pushed into the exit 74 for the abrasive grains guided by the inner wall (upstream wall) 78 of the exit 74. Accordingly, the grains that are pushed into the exit 74 converge there. Thus they are moved onto the blades 51 of the impeller 53 in a high density through the exit. As a result, the area against which the grains are thrown by the impeller 53 in a fan-like form can be narrower than that resulting from a conventional impeller.

FIG. 10 compares of the area at which abrasive grains are thrown in a fan-like form using the exit 54 or 74 for the abrasive grains of the control-cage 55 or 75 of the present invention to an area that uses another type of exit for the abrasive grains of the control-cage.

FIG. 10 shows that the area at which abrasive grains are thrown in a fan-like form using the exit 54 or 74 for the abrasive grains of the control-cage 55 or 75 of the present invention is narrower than that of another type of exit for the abrasive grains of a control-cage.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of the centrifugal shot-blasting device using the control-cage of an embodiment of the present invention.

FIG. 2 is a radial cross-sectional view of the control-cage of FIG. 1.

FIG. 3 is a radial cross-sectional view of another control-cage.

FIG. 4 shows distributions of the thrown media of an embodiment and comparative examples 1 and 2.

FIG. 5 is a radial cross-sectional view of a conventional control-cage.

FIG. 6 is a schematic cross-sectional view of the control-cage of an embodiment of the invention of claim 8.

FIG. 7 is a front view of FIG. 6.

FIG. 8 is a partial cross-sectional view of the centrifugal shot-blasting device using the invention of claim 8 or 9.

FIG. 9 is a schematic cross-sectional view of an embodiment of the control-cage of the invention of claim 9.

FIG. 10 is a graph that compares the areas at which abrasive grains are thrown in a fan-like form using the exit for the abrasive grains of the control-cage of the present invention to that using another exit for the abrasive grains of the control-cage. 

1. A control-cage used for a centrifugal shot-blasting device that rotates an impeller having a plurality of blades at high speed, and throws shot-blasting media through the opening of the control-cage by means of the blades, which control-cage is cylindrically shaped and is placed inside the impeller, wherein the opening of the control-cage is made by cutting out the cylindrical part of it in parallel with its central axis, has a quadrangular shape and lateral walls (an upstream wall and a downstream wall) located upstream and downstream of the direction of the rotation of the impeller, and wherein the upstream wall is made so that the angle between a plane containing the axis and the plane containing both the axis and the inner edge of the upstream wall is larger than the angle between the plane containing the axis and the plane containing both the axis and the outer edge of the upstream wall when they are measured in the direction opposite the direction of the rotation of the impeller.
 2. The control-cage of claim 1, wherein the upstream wall and the downstream wall are parallel to each other.
 3. The control-cage of claim 1 or 2, wherein the upstream wall is made so that the wall would be the tangential line of the inner periphery of the control-cage if the control-cage were to be cut radially.
 4. The control-cage of claim 3, wherein the downstream wall is made so that the angle between a plane containing the axis and the plane containing both the axis and the inner edge of the downstream wall is larger than the angle between the plane containing the axis and the plane containing both the axis and the outer edge of the downstream wall when they are measured in the direction opposite to the direction of the rotation of the impeller.
 5. The control-cage of claim 1 or 2, wherein the downstream wall is made so that the angle between a plane containing the axis and the plane containing both the axis and the inner edge of the downstream wall is larger than the angle between the plane containing the axis and the plane containing both the axis and the outer edge of the downstream wall when they are measured in the direction opposite to the direction of the rotation of the impeller, and wherein the difference between the angles is 0-35 degrees, in which one angle is between the plane containing the axis and the plane containing both the axis and the outer edge of the upstream wall and the other is between the plane containing the axis and the plane containing both the axis and the inner edge of the downstream wall.
 6. A centrifugal shot-blasting device comprising a housing, a driving means that is installed outside of one of the lateral sides of the housing, an impeller that has a plurality of blades and that is fitted onto the driving shaft of the driving means, a distributor that is placed inside the impeller, that is concentrically fitted onto the driving shaft and that has almost equally-spaced openings in its circumference, the control-cage of claim 1, 2, 3, 4, or 5, wherein it is fitted on an inlet that is provided on another lateral side of the housing, and an inlet tube that is fixed on the housing so as to let shot-blasting media be supplied to the inlet.
 7. The centrifugal shot-blasting device of claim 6, wherein the impeller comprises a lateral plate of the driving shaft of the driving means, a lateral plate that is located on the side of the inlet tube and apart from the lateral plate of the driving shaft at a given distance, and that has an opening at its center that is larger than the circumference of the control-cage, and a plurality of blades that are radially fixed between the lateral plate on the side of the inlet tube and the lateral plate on the side of the driving shaft.
 8. A centrifugal shot-blasting device for throwing abrasive grains comprising an impeller that can rotate and that has a cylindrical space in its middle, a control-cage that is nearly cylindrical and that is fixed inside the space and that has an exit for abrasive grains on its cylindrical part to discharge the grains, and a distributor that is located inside the control-cage so that it can be rotated together with the impeller, wherein the exit for abrasive grains on the control-cage is approximately an elongated slit that has a given width and that is parallel to the central axis of the control-cage, and has an upstream wall that is located upstream of the direction of the rotation of the distributor, and a downstream wall that is located downstream of the direction of the rotation of the distributor, and wherein the upstream wall is inclined to the direction of the rotation of the distributor at 30-90 degrees to the line that is orthogonal to the central axis and that crosses the inner edge of the upstream wall.
 9. A centrifugal shot-blasting device for throwing abrasive grains comprising an impeller that can rotate and that has a cylindrical space in its middle, a control-cage that is nearly cylindrical and that is fixed inside the space and that has an exit for abrasive grains on its cylindrical part for discharging the grains, and a distributor that is located inside the control-cage so that it can be rotated together with the impeller, wherein the exit for abrasive grains on the control-cage is approximately an elongated slit that has a given width and that is parallel to the central axis of the control-cage, and that has an upstream wall that is located upstream of the direction of the rotation of the distributor, and a downstream wall that is located downstream of the direction of rotation of it, and wherein the upstream wall extends along an almost tangential line of the inner periphery of the control-cage.
 10. The centrifugal shot-blasting device for throwing abrasive grains of claim 8 or 9, wherein the downstream wall is inclined to the direction of the rotation of the distributor at 30-90 degrees to the line that is orthogonal to the central axis and that crosses the inner edge of the downstream wall.
 11. The centrifugal shot-blasting device for throwing abrasive grains of claim 8, 9, or 10, wherein the downstream wall is approximately parallel to the upstream wall.
 12. The centrifugal shot-blasting device for throwing abrasive grains of claim 8, 9, 10, or 11, wherein the given width of the exit for abrasive grains is determined so that the angle between the line that is orthogonal to the central axis and that crosses the outer edge of the upstream wall and the line that is orthogonal to the central axis and that crosses the inner edge of the downstream wall is 0-35 degrees.
 13. The centrifugal shot-blasting device for throwing abrasive grains of claim 8 or 9, wherein the elongated slit of the exit for the abrasive grains includes a quadrangular opening. 